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STRUCTURAL OVERVIEW OF THE NERVOUS SYSTEM

  1. Anatomical terminology.

    1. Below the level of the midbrain, rostral and caudal denote toward the “head” and “tail,” respectively. Above the midbrain, rostral indicates toward the front of the brain (anterior), and caudal indicates toward the back of the brain (posterior).

    2. Below the level of the midbrain, dorsal and ventral indicate toward the back and front of the body, respectively. Above the midbrain, dorsal refers to the top (superior) surface of the brain, and ventral refers to the bottom (inferior) surface of the brain.

    3. Anterior and posterior indicate toward the front or back of the body (or brain), respectively.

    4. Superior and inferior indicate toward the top of the cerebral cortex or the sacral end of the spinal cord, respectively (Figure 2-1).

    5. The median sagittal plane divides the nervous system into two equal halves in the anterior-posterior plane, with the left and right sides being the mirror image of each other.

      1. Medial and lateral indicate toward or away from the midline, respectively.

      2. Ipsilateral indicates two points on the same side of the midline; contralateral indicates two points on opposite sides of the midline.

      3. Coronal “slices” are vertically oriented at ninety degrees to the sagittal plane.

      4. The horizontal plane is perpendicular to both the sagittal and coronal planes.

  2. Neurons have two general components, the soma and neurites (Figure 2-2):

    1. The soma (cell body) contains the cell nucleus and the rough endoplasmic reticulum.

    2. Neurites are thin cellular processes extending from the soma:

      1. The axon is the cellular process that carries action potentials away from the soma. Axons are often long and may have multiple branches.

      2. Dendrites have a structure similar to axons but receive impulses from other neurons. Many neurons have an extensive set of dendrites, referred to as the dendritic tree.

  3. Divisions of the nervous system.

    1. The nervous system can be divided into the central nervous system (CNS) and the peripheral nervous system (PNS).

    2. The CNS is enclosed within the meninges and consists of the brain and spinal cord.

    3. Structures in the PNS are outside the meninges and include spinal nerves, cranial nerves, pre- and post-ganglionic autonomic nerves, and sensory receptors.

    4. The meninges is the collective term for three membranous layers enclosing the CNS:

      1. The dura mater is the outermost layer and consists of tough connective tissue.

      2. The arachnoid mater is the middle layer and lies beneath the dura, which it closely follows. The subarachnoid space lies beneath the arachnoid membrane and is filled with cerebrospinal fluid (CSF).

      3. The pia mater is the innermost layer. It is a delicate vascular membrane that closely follows the surface of the brain and spinal cord.

      4. imageThere is normally no space between the cranial dura and the bony skull. The cranial dura has a double layer, with one layer adhered to the inside of the skull bones. Head trauma may force blood between the bone and dura mater, known as an epidural hematoma. In contrast, the spinal cord has ...

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